1. Field of the Invention
The present invention relates to a window for automobiles or the like, including a window plate and a frame member composed of a thermoplastic synthetic resin material and provided integrally with the window plate, and also to a method of manufacturing such windows.
2. Description of the Related Art
Automobile windows wherein a window plate is integrally provided with a frame member composed of a thermoplastic synthetic resin material is advantageous in that, since it is not necessary to prepare a window molding member as a separate component from the window plate, the number of components and assembly steps can be reduced to realize an improved manufacturing productivity in the assembly lines of automobile factories.
There is disclosed, e.g. in U.S. Pat. No. 4,139,234 and Japanese Patent Application Laid-open Publication Nos. 56-99,817 and 57-1,737, a method of manufacturing such automobile windows wherein the peripheral edge of a window plate is placed in an injection mold including upper and lower mold halves, and a molten thermoplastic synthetic resin material is injected into the cavity space between the upper and lower mold halves through at least one gate. While the above-mentioned method permits formation of an integral frame member along the edge of the window plate, a number of problems are left still unsolved, which are as follows.
First of all, thermoplastic synthetic resin material may have a relatively high viscosity during the injection into the mold cavity, which depends upon physical and/or chemical properties of the material. Then, the injection has to be carried out at an elevated temperature of the mold to lower the viscosity of the resin material and to avoid premature cooling of the resin material before it has been completely distributed within the mold cavity has to be carried at and under a relatively high injection pressure to realize a uniform distribution of the resin material throughout the entire cavity space. The elevated temperature to which the mold has to be heated necessarily requires a longer time until completion of the injection and cooling of the resin material, and makes it difficult to achieve an improved manufacturing productivity. Furthermore, the relatively high injection pressure often results in undesirable formation of burrs or flushings along the parting surface of the mold halves or results in damage to the window plate due to a higher tightening force applied from both sides by the mold halves for withstanding the injection pressure. Also, when the frame member is provided with an integral, strip-like ornamental element applied on its outer surface with clips or with the like fitting elements partly embedded in the synthetic resin material by a so-called insert-molding process, these elements may be deformed or subjected to dislocation by the injection pressure.
Secondly, the frame member placed to cool is more or less accompanied by shrinkage, thereby subjecting the window plate to a severe compression stress. Thus, when the window plate is composed of a brittle glass plate, it is not always possible to prevent formation of cracks in the window plate. Particularly, when the window plate has a surface curvature, the window plate is often subjected to a substantial bending stress, and the curved surface of the window plate undergoes an undesirable deformation. These problems are more significant when the window plate is composed of a transparent synthetic resin material with a relatively lower structural rigidity than inorganic glass. Moreover, the frame member is generally formed to surround the edge of the window plate from both sides thereof, and thus includes a substantially U-shaped cross-sectional portion formed of relatively thin lip and web sections on the outer and rear surfaces of the window plate, respectively, and a relatively thick bridge section for connecting the lip and web sections with each other. The material thickness of the frame member with such a sudden change results in a retarded cooling rate of the thick bridge section and results in a resultant formation of sink mark on its outer surface.
Finally, in addition to the above, the window A plate is accompanied by certain dimensional fluctuation which are due to practical difficulties in preparing window plates of a satisfactorily constant shape, while the volume of the mold cavity remains always constant. An optimum amount of thermoplastic synthetic resin material to be injected into the mold cavity thus varies for each window plate, depending upon the length with which the window plate is inserted into the mold cavity. From practical viewpoint, however, it is not very appropriate to individually adjust the amount of the resin material for each shot, and it has thus been a general practice to inject into the mold cavity a substantially constant amount of resin material, without regard to dimensional fluctuation of the window plate at all. It is of course that injection of an excessive amount of resin material into the mold cavity, too, results in formation of burrs or flashings along the parting surface of the mold halves, while insufficiency in the injected amount of the resin material gives rise to a undesirable tendency of the sink mark to appear on the outer surface of the frame member.
It is therefore a primary object of the present invention to provide a novel and improved window for automobiles or the like, which includes a frame member formed integrally with the window plate and composed of a thermoplastic synthetic resin material and which can be readily manufactured without the above-mentioned drawbacks.
Another object of the present invention is to provide a novel and improved method of manufacturing windows for automobiles or the like, including a frame member formed integrally with the window plate and composed of a thermoplastic synthetic resin material, by which the windows can be readily manufactured without the above-mentioned drawbacks.
According to one aspect of the present invention, there is provided a window for automobiles or the like, including a window plate, and a frame member which is composed of a thermoplastic synthetic resin material and formed into an integral structure with the window plate along at least one edge thereof, wherein said frame member includes a substantially U-shaped cross-sectional portion comprising lip and web sections which are spaced from and opposed to each other on outer and rear surfaces of the window plate, respectively, and a bridge section connecting the lip and web sections with each other, wherein said bridge section has a longitudinally continuous hollow inner space.
According to another aspect of the present invention, there is provided a method of manufacturing windows of the above-mentioned structure, comprising the steps of:
(A) preparing a window plate;
(B) preparing a mold having surfaces defining a cavity of a predetermined volume therein, said cavity being of a configuration which corresponds to said frame member;
(C) placing at least one edge of the window plate in the mold cavity;
(D) injecting into the mold cavity a predetermined amount of thermoplastic synthetic resin material in its molten state, said amount being smaller than said volume of the cavity;
(E) injecting compressed gas into the synthetic resin material in said cavity to urge said synthetic resin material against said surfaces of the mold defining the cavity; and
(F) placing said synthetic resin material under cooling and solidification in said mold cavity, thereby to form a frame member which is integral with said window plate along at least one edge thereof, and which includes a substantially U-shaped cross-sectional portion formed of lip and web sections which are spaced from and opposed to each other on outer and rear surfaces of the window plate, respectively, and a bridge section connecting the lip and web sections with each other and having a longitudinally continuous hollow inner space.
The window according to the present invention, including a frame member which is integral with the window plate and whose bridge section connecting the lip and web sections with each other has a longitudinally continuous hollow inner space, and serves to effectively protect the window plate from damages or deformation upon shrinkage of the frame member after it has been formed, without being subjected to severe compression and/or bending stress, due to the deformability of the hollow inner space in the bridge section of the frame member.
Furthermore, in the method of manufacturing the windows according to the present invention, the frame member is formed by injecting into the mold cavity a relatively small amount of thermoplastic synthetic resin material as compared with the volume of the cavity and by injecting the compressed gas into the synthetic resin material in the cavity. Thus, even a synthetic resin material with a relatively high viscosity can be uniformly distributed throughout the cavity without application of a higher injection pressure as is the case in conventional injection process. Moreover, the synthetic resin material in the mold cavity can be sufficiently urged by the injected compressed gas against the surfaces of the mold defining the cavity to realize a desired configuration of the frame member without an undesirable sink mark.